Mine (2007) went without AM radio for 2 years - the dealer service guy just kept telling me that no a.m. radio was "normal" for this model. (Apparently a lot of stuff is normal for this model...)
I finally insisted -- they brought in an Aston Audio specialist and kept it two days and now it's fine. Though I do now have periodic problems like it auto-muting while driving. A guy I know with a DB9 who bought the same week as me has had speakers muting since his was new, too. He's a mechanic and took it apart and found a bad cable going past the subwoofer that was being pinched and causing his probs.